Osmosis investigation. My prediction is that as the concentration of the solute increases, net flow will increase out the potato

by specialkay (student)

Osmotic potential in potatoes.

Introduction:

Osmosis is the diffusion of water from a high concentration to a low concentration through a semi-permeable membrane. This process does not require energy (passive transport) as it works through pressure to reach equilibrium, i.e. the same concentration on both sides, and in this case the solute concentration would be equal and the solutions would be isotonic at the end- in this case there is no net flow of water through the membrane.

There are two main types of solutions in regards to osmosis.

e.g's

-A hypotonic solution is a solution with a lower concentration of solutes compared to another. A cell in a hypotonic solution has a higher concentration of solutes than the surrounding solution, causing water to flow into the cell. Cells can burst (cytolysis) in some cases.

-A hypertonic solution is a solution with a higher concentration of solutes compared to another. A cell in a hypertonic solution has a lower concentration of solutes than its surroundings, leading to a decrease of water in the cell. Water will leave the cell by means of osmosis, this can lead to plasmolysis, whereby a cell loses turgor pressure and the protoplasm (yellow in diagram) peels away from the cell wall. The effect of this is a plant will wilt if too many cells lose turgor.

The factors affecting osmosis rate are:

Temperature.

The molecules in the solutions move faster with a higher temperature, therefore the frequency of collisions increases meaning quicker osmosis.

Concentration gradients between solutes (osmotic gradient)

[Basically] Because a hypotonic solution has a smaller solute concentration, there is a higher water concentration, which means there are more collisions with the membrane than the hypertonic solution causing a faster net flow to the hypertonic solution.

Surface area to volume

A small cell has a large SA:V ratio and therefore can exchange molecules with it's external solution rapidly, because there are more H2O collisions with the membrane due to the high ratio, however the probability of successful osmosis is not increased. Ions and water can be lost by diffusion and osmosis, and heat can be lost at a faster rate.
A large cell has a small SA:V ratio and therefore exchanges molecules with it's external solution slowly, because there are less collisions with the membrane due to the smaller ratio.

The factor I chose:

I choose osmotic gradient as my independent variable, because it's the easiest variable from which to produce reliable, accurate and reproducible results. I didn't chose SA:V as the independent variable, because of the time it takes to prepare that amount of potato to meet a good standard precision, it would simply take to long to repeat the experiment for reliability. I could have chosen to use temperature as a variable, however I felt it would be wiser to chose otherwise, because if I used a tube in a water bath it would take too long to perform the experiment, as it would take too long for the tube to heat up and if I simply put hot water in a tube and waited for it to cool down, that too would take too long. Additionally the membrane may be altered by the heat, which technically is unfair to the test, because the membrane should be a controlled variable. So, I chose concentration.

Hypothesis and Prediction:

My prediction is that as the concentration of the solute increases, net flow will increase out the potato. At first I hope to see that the net flow will be into the potato until equilibrium is reached, after this point as concentration increases the net flow will be out the potato. I believe this because of particle theory- that the solution with the highest concentration of water molecules will diffuse through the partially permeable membrane faster than the other side due to the greater amount of water molecules colliding with the membrane; this applies to my prediction- as the lowest concentration of water is in the potato at first the water will flow in and as concentration of water in the solution decreases the two solutions will reach equilibrium. After that, the outer solution will have a smaller concentration of water thus the potato will lose water, thus losing water weight (similarly the potato will gain water weight at the beginning too).

Method

Preliminary Work:

Plan:

Equipment:

Test tube rack
5 Test tubes
3 Measuring cylinders
1 bottle of distilled water (bottles to be shared, amount to use: 50ml)
1 bottle of sucrose solution (bottles to be shared, amount to use: 50ml)
1 or more potatoes, enough for 5 pieces
1 core-borer (size to be used unknown as it depends on which one I can aquire)
1 scalpel
1 cutting tile
Paper towel
1 stop watch
Weighing scales

Techniques:

First I will set up the test tubes in the rack and then I will prepare the solutions.

1. I chose 3 measuring cylinders for this purpose; I will use two of them to quantify the sucrose solution and the distilled water, leaving the third to add the two mixtures together. This extra effort saves time and keeps precision, as there is no need to make repeat solutions as every thing is correct before they are mixed leaving an accurate and precise mixture. To make my solutions of 0, 0.25, 0.5, 0.75 and 1 mole sucrose, I will use ratios- e.g. for 0.5: 1:1, so 10ml of each.

Next I will prepare the potato pieces for their "soak".

2. I will aim to attain all the pieces from one potato. I will take the potato lay it on the tile and bore downwards with the tool. Once I have 5 separate cylinders of potato I will roll them on the paper towel to soak the excess moisture. Thereafter I will weigh them and cut them down till they are 1.00 gram each. Part of this technique is cutting of slivers from the cross section of the cylinder so that they maintain a similar surface area. The next step will be to put the pieces in each solution, while my partner starts the watch on the time the first piece is added.

While the potatoes soak, I will replace the equipment.

3. Once the 20 min time period for the potatoes is up I will drain all the tubes in a manner so that the potato pieces are still in their tubes. I will take them to the scales and one at a time I will roll them on paper towel to soak up excess (undiffused) moisture and then weigh them.

Once I have the results I will write them into my pre-drawn table, then dispose of the potato.

The results of the preliminary experiment are as follows:

...

This is a preview of the whole essay

While the potatoes soak, I will replace the equipment.

Once I have the results I will write them into my pre-drawn table, then dispose of the potato.

The results of the preliminary experiment are as follows:

Variable control:

The potato used- this could mean different beginning solute concentration in the potato, rendering the results less reproducible.
The amount of solution used- affects osmosis directly
The amount of time each potato will soak for- affects how long osmosis can occur for
The dryness of the potato when weighed- affects accuracy of results
The weighing scales- could mean less precise results and also less reproducible results
The surface area of potato- this can affect SA:V ratio in osmosis reducing reliability of results.

The Main Plan:

Equipment:

Test tube rack- there isn't a better alternative for the same purpose. My only principle was that it is easier to keep track of the potatoes when they are in a rack.
5 Test tubes- as I wrote before there aren't too many pros/cons when it comes to containers, apart from my earlier point- test tubes utilise racks, alternatives would be wider glass cylinders however, I find it easier to see any mistakes in the measured solutions when they are in a thinner container. An argument against the tubes may be that they make contact with the side of the glass which can divert any osmosis, however I find that the case with the wider containers, because they are more shallow meaning they more often touch the bottom rendering the earlier point mute.
3 Measuring cylinders- these are precise and worked well in the preliminary investigation, alternatives could be wider cylinders, however I find that the thinner ones marginalise any errors in my measuring, if any, as errors are noticeable all the same but smaller, thus yielding better precision.

1 bottle of distilled water (bottles to be shared, amount to use: 50ml)- the specific bottle in question has a straw, which can squeeze out drops of the liquid. I find this better than most pieces of equipment for dispensing as using drops can make it easier to attain precision through measurement. Pipettes are an alternative, however I find that to fill a tube solely with one would be too time consuming, as would a burette with the preparation of one.
Pipette- even though I said they are time consuming, I used one to make up the difference when my measuring was short, which was incredibly useful to improve my precision in measurement.
1 bottle of sucrose solution (bottles to be shared, amount to use: 50ml)- this container is a 1 liter vial, they are ok in terms of pour control and have a thin neck which helps with flow however I found it laborious to pour with, nonetheless with the use of three measuring cylinders I could keep attempting until a satisfying precision was attained.
1 or more potatoes, enough for 5 pieces. It would be ideal to use one potato as different potatoes have different sugar levels, which greatly affects osmosis in the pieces of potato.
1 core-borer (size to be used unknown as it depends on which one I can acquire)- a very good method of attaining similar samples of potato. Simply cutting bits off of a potato is vastly inferior to using a bore, because of the imperfection in my scalpel strokes making a borer more precise.
1 scalpel- a useful tool, sharper than most knives and cuts well, meaning better sizing of the potato pieces for the experiment.
1 cutting tile- nothing else is needed. Thinking of an alternative is not necessary.
Paper towel- to dry the potatoes, as before there is no need for an alternative.
1 stop watch- They are precise at keeping a timer and have a reasonable alert feature, no need for an alternative.

Weighing scales- there aren't many alternatives, perhaps displacement, but the trade off for scales is silly. It would be sensible to use better higher grade scales as the current scales work to 2dp and as most of the results change by the 100th it is good assumption to say that a 3rd decimal place would yield a better precision of results.

Techniques:

First I will set up the test tubes in the rack and then I will prepare the solutions. I think it is better to set up the soak for the potatoes first so that when the potatoes are prepared they aren't idle in a dry environment, in the case of leaking or mistakes such as if they were dropped on the floor.

1. I will use 3 measuring cylinders for this purpose; I will use two of them to quantify the sucrose solution and the distilled water, leaving the third to add the two mixtures together. This extra effort saves time and keeps precision, as there is no need to make repeat solutions as every thing is correct before they are mixed leaving an accurate mixture. To make my solutions of 0, 0.25, 0.5, 0.75 and 1 mole sucrose, I will use ratios- e.g. for 0.5: 1:1, so 10ml of each. From the preliminary investigation I found the range of values appropriate as they yielded a good range of results, which apply to my prediction and hypothesis. The range is also appropriate because there isn't a less concentrated solution than 0 mole, so working up from there is perhaps the only way to attain results that meet my prediction.

Next I will prepare the potato pieces for their "soak".

2. I will aim to attain all the pieces from one potato; because of the aforementioned reasons I decided to cut the potato in half so that it rests on the tile making it easier to get cylinders and it is more efficient with potato. I will take the potato lay the flat side on the tile and bore downwards with the tool. Once I have 15 separate cylinders of potato I will roll them on the paper towel to soak the excess moisture. Thereafter I will weigh them and cut them down till they are 1.00 gram each. Another improvement on technique will be to dry the freshly cut section of the potato to maximise the effectiveness of weighing the potato. Part of this technique is cutting of slivers from the cross section of the cylinder so that they maintain a similar surface area, this is to control surface area as a variable.

The next step will be to put the pieces in each solution, while my partner starts the watch on the time the first piece is added.

I decided to do 2 repeats of each solution to increase validity and reliability.

While the potatoes soak, I will replace the equipment.

3. Once the revised 30 min time period for the potatoes is up I will drain all the tubes in a manner so that the potato pieces are still in their tubes. I will take them to the scales and one at a time I will roll them on paper towel to soak up excess (undiffused) moisture and then weigh them.

The reason I upped the time to thirty minutes is to get the most osmosis to have clear ranges to draw conclusions from.

Once I have the results I will write them into my pre-drawn table, then dispose of the potato.

Variable control:

The potato used- this could mean different beginning solute concentration in the potato, rendering the results less reproducible.
The amount of solution used- affects osmosis directly
The amount of time each potato will soak for- affects how long osmosis can occur for
The dryness of the potato when weighed- affects accuracy of results
The weighing scales- could mean less precise results and also less reproducible results
The surface area of potato- this can affect SA:V ratio in osmosis reducing reliability of results. I will try to control this by using the same weights for all the potato pieces, as they should be at least similar if they weigh the same.

Risk assessment form

Results:

Table of results:

Outlier:

I've selected 0.79 as an outlier for a few reasons. Firstly it is far out of the ranges in my other results, I think that it is far astray from the true value because of this. Secondly that would mean the ranges of 0.75 and 1 overlap greatly which could suggest that they have the same or a similar true value, which I doubt given the current results and ranges in them (and due to the theory behind osmosis). Finally I think it is an outlier because, it is not reasonably close to the other results in the same solution.

Problems in data collection:

I found there to be not many problems with collection in regards to technique. One problem was that some potatoes got perhaps 10-20 seconds more in the solution, which admittedly isn't much yet it is improper control of variables, which affects the fairness of the test. In regards to equipment I found the scales to be inconsistent when I placed the potato on the weighing tile, by this I mean they wouldn't settle on a single value very easily, so when I took the readings it is possible that the scale had not set on the final value.

Secondary results:

This is a similar experiment using sodium chloride(aq) instead of sucrose solution. It was from a group working in the same class as me courtesy of Isobel Edmondson.

This is an experiment that shows water lost through osmosis in beetroot tissue. This was provided by OCR exam bored in 'CONTOLLED ASSESSMENT INFORMATION FOR CANDIDATES (2)' on page 3.

Conclusion:

For my main results I've drawn that as the concentration of the sucrose solution increases the weight of the potato decreases. I think this is down to the solutions increasing in solute concentration. From 0 the solution was hypotonic leading to flow into the cell, from that point the solution became less hypotonic leading to less net flow into the cell (at 0.25) then as the solution reached 0.5 mole, the solution became hypertonic leading to net flow out of the cell. This all is congruent to my conclusion. As for the implications of this experiment, I have learned more about osmosis and the rate of osmosis.

Evaluation:

Improvements to equipment:

My foremost improvement would be the scales due to the fact that they were limited to two decimal places, which I contrive to be a severe impediment on data collection due to the variation happening by the 100th, which leads me to believe a lot more accuracy could be gained by having scales that at least read to the 1000th. However in terms of an improvement to the actual equipment I'm afraid there isn't much I can suggest, because the problem is just typical of older scales. If I could I would have more advanced scales as an improvement I believe this would increase precision in my results, as the added decimal places would be closer to the true values. The other qualm I have with the scales is that they fluctuate their values often, of which I'm not aware of a solution, however I think that is still worthy of a mention as something I would improve.

Furthermore I could have used a burette for measuring the sucrose solution and water to have more precise mixtures, which would bring the results closer to the true values as osmosis is affected by the solution concentration.

I would also have the borers ends straightened out as they are turn inwards slightly which causes and uneven surface, which affects the control of, surface area of the bored potato. This improvement would make a fairer test, because of the improvement in variable control.

Next I would suggest having a stopwatch for each solution test tube to ensure that the control of time in the solution to make a fairer test, yet I wouldn't improve the stop watches individually.

Improvements to method:

For the timing I would soak each potato at 5 minute intervals (for 30 mins still) so that they all have an equal soak and I can tend to them in the same manner I would the rest. I think this would improve fairness, because then I wouldn't have the remaining potatoes waiting while I weigh the others and cut the others etc. This would cover many areas of variable control such as time in solution, time out of solution...

I think that weighing all the potatoes laid on the cross section of the cylinder will improve accuracy, because of the temperamental nature of the scales, using the same 'position' may be another variable to be controlled, which may increase precision and accuracy, as the previous potatoes were placed on the scale with no control.

Another method I would introduce if I were to repeat the experiment would be to cut the potatoes to the same length at the beginning and then weigh them, so I would have different starting weights, but the same surface area and in hindsight I think this would make a fairer test than making them weigh the same, as osmosis will be the same in all the potatoes this way. This would also solve my scale problem, because I wouldn't have to try and attain a weight so I could cut the use of the scales down by just weighing them once rather than cutting the potato down which requires multiple weigh-ins before I'm satisfied with the weight.

Accuracy and repeatability:

Ranges and line of best fit:

I think that the smaller size of my range bars shows that my results should be close to the true value, also because of the consistent ranges. However I think they aren't considerably close to the true values because of the lower precision of the experiment due to factors such as the scales and my method surrounding that affecting the accuracy.

Individually I think the 0, 0.25 and 1 mole concentrations are the most accurate and close to the true value because of the ease I could draw a line of best fit in them and so close to the averages as well. I think this boosts the accuracy in these three points and also the overall repeatability of these results.

For the 0.5 and 0.75 concentrations I think that they were so lower than one would expect from the trend, because I used a different set of scales for those sets of results because the other scales were in use. It's possible this set of scales weighed differently.

0.5 and 0.75 did not fit a line of best fit and I feel this is a result of the different scales. I believe this affects the accuracy and repeatability negatively, so much so that I think these two sets will be unrepeatable, however I do not believe these sets are outliers, because it could also be the rate of osmosis playing a part.

I've selected the 0.79 result as an outlier from before and as my explanation for it I think it was a trimmed piece that I had miss taken for the piece I meant to use resulting in a lighter piece than the rest. Despite this I still have confidence in the rest of my results because ranges and general trend of them.

Secondary results:

Secondary result analysis:

For the first shown piece of secondary results (sodium chloride(aq) experiment) the weight of the potato increases as the concentration of salt increases due to osmosis also. This also uses the same theory that I have used for my experiment and it, too, is congruent with my hypothesis and prediction in how the net flow goes from into the potato to outwards.

My confidence level in this piece is a 6/10 because of the sheer size of the range bars, which shows that the results aren't very precise; in particular I would like to highlight the 3% concentration result, because of it's length it shows me that these results aren't very close to the true values.

When I tried to give this graph a line of best fit I did so with difficulty because the middle points dip, similar to my results in the midsection, so I had to let these points pull the line across. I think a curve of best fit may have been an option, however I have my doubts about the "dipped" points being close to the true value, so I chose not to use a curve. Again the fact that the range bars are so long makes me not want to use a curve, on account of the reliability of this source.

This source supports my work, because of the similar trend in the results, like how the net flow has a negative correlation with the concentration and the fact it's the same experiment with a different solution. Additionally this set has a dip in the results, which supports mine, whether or not I question the accuracy of these 'dips'. This also supports my hypothesis, because it's the same theory due to the fact the only difference is solute. Yet the ambivalence of the results means that it's support of mine only boosts my confidence in my primary data a little. However this source undermines my choice for a line of best fit, because I maintain that the 'dips' in the mids of the results was inaccuracy.

My second secondary result table in effect shows the second half of both of the other results, because the second halves both show water loss. This result set also shows that as the concentration of sucrose increases water levels decrease. This is very similar to my results too.

This source is investigating 'effects' of sucrose concentration, the fact that osmosis is affected by concentration means that these results should show the same trend as my results since the osmosis shouldn't change. The water loss is very similar to the latter parts of my results, however this source shows water loss in cells not in weight, also the water loss is very abrupt and severe unlike my results. Obviously this set is investigating beetroot which may be very different to potato, despite this the water loss is similar and the osmosis is in common so I still view it as relevent. Other than that these results can be used to support my prediction and hypothesis all the same as mine.

I'm not very confident in these results though, because there are no repeats of the values, although the results do fit a curve, which appears in all three of the result sets. This boosts my confidence a little, however this factor does not mean this data is reliable. Over all I would say my confidence in this set is 5/10.

I would say these results support mine and extend mine. The support comes from the similar water loss and the same solution used. The extension is that it continues till all the cells lose water, which is not featured in my results. However this source also undermines my choice for a line of best fit, because I maintain that the 'dips' in the mids of the results was inaccuracy.

Further data:

To be surer of my conclusion I would need more investigations and results run under the improved conditions I have written about, with concentrations above 1 mole. I think this is the case because of my lack of confidence in all data sets.

Summary:

I still believe my prediction accounts for all the data collected, because of the beginning solutions being hypotonic thus the net flow was into the potato, this is shown in weight gain in the sucrose and sodium chloride sets and the cell water loss set, while there is no water lost which supports this. Then the concentrations jump over the isotonic stage in the two osmotic potential investigations to the point where the solution is hypertonic meaning the osmosis is faster out of the potato; this is supported by the loss of weight in the two weight experiments and the water loss in the beetroot experiment.

I feel that my conclusion is quite valid due the similar trend in the other potato experiment and the similar water loss in the beetroot. Furthermore it turns out all the results had the curve which backs up my results and therefore the accuracy and validity. Overall I found my accuracy to be satisfying, despite my lack of confidence in it. I managed to explain away my only outlier and my ranges were tight meaning they could be very close to the true values.

As for further work to assure me of my conclusion to the hypothesis, I would like to qualitatively observe osmosis through a microscope with multiple solution concentrations. I would also like to repeat my experiment under the improved parameters to add confidence to my results which back up the conclusion and validity of my hypothesis, because that is the theory in practice.

Osmosis investigation. My prediction is that as the concentration of the solute increases, net flow will increase out the potato

This is a preview of the whole essay

Document Details

Related Essays

Osmosis, I predict the mass of potato will first increase then start decrea...

Investigate the cell sap concentration of solute in a potato chip using osm...

Determine the water potential of potato tuber cell with the varying affect...

Potato and Osmosis Investigation.